Such a method is generally known from the prior art. This generally involves providing an electrically conducting support with an adhesive film, before the electronic components are fitted. This can easily be done without any risk of damaging the electronic components. Integrated circuits, for example, are very fragile components which are easily damaged. The very thin gold connecting wires in particular are susceptible to damage.
After the adhesive films have been applied, the electronic components are attached to the support, for example by cementing (die-bonding). This is often done by means of an epoxy adhesive which requires curing at elevated temperature. Such a temperature increase is found to impair adhesion of the adhesive film.
Then the connecting wires of the electronic components are electrically connected to the electrically conducting support, for example by welding (e.g. thermosonic), soldering or the like (wire-bonding). This temperature increase too is found to impair adhesion of the adhesive film.
In the present application, the term “electrically conducting support” refers, for example, to a lead frame. A lead frame is a metal support which comprises many very fine leads which are connected to the connecting wires of the electric components. It will be evident that if an adhesive film has been bonded to one side of such a lead frame, any actions having adverse impact on adhesion should be avoided, since such leads easily become detached from the adhesive film, with all the adverse consequences thereof.
Then the support with adhesive film and electronic components is introduced into a mould, a so-called transfer-moulding technique often being employed to encapsulate the electronic components on the first side of the support in one or more mould cavities with an encapsulating material (compound). During encapsulation, any contact of the encapsulating material with the second side of the electrically conducting support should be avoided. Those electrically conducting areas of the support which were left free on said second side of the support serve for electrical connection of the electronic components at the time of their ultimate use.
Finally, the adhesive film is removed and the encapsulated electronic components are separated from one another along cutting lines, after which they are suitable for further processing.
If the leads or other parts of the lead frame are not unambiguously bonded to the adhesive film, there is the possibility of encapsulating material penetrating between the adhesive film and the lead frame during encapsulation. As a result, electrically conducting areas can become insulated, thereby rendering subsequent electrical connection impossible. In the prior art, bonding between the adhesive film and the support is not unambiguous and reproducible, since the many heat treatments (attaching of electrical components and electrically connecting them to the support) often leads to locally reduced adhesion of the adhesive film. It is also possible for parts of the support to become detached from the adhesive film owing to a difference in expansion coefficient between the support and the adhesive film during heating or cooling operations.
Equally, it is advisable, of course, to keep handling of the support with an adhesive film thereon to a minimum. Any movement, bending or the like of the support with the adhesive film thereon may induce local detachment of the adhesive film from the support.